It is well known, particularly in the field of transporting and using particulate materials, commonly powders, granules, pellets, and the like, that it is important to keep product particles as free as possible of contaminants. Particulates are usually transported within a facility where they are to be mixed, packaged or used in a pressurized tubular system that in reality produces a stream of material that behaves somewhat like a fluid. As these materials move through the pipes, considerable friction is generated not only among the particles themselves, but also between the tube walls and the particles in the stream. In turn, this friction results in the development of particle dust, broken particles, fluff, streamers (ribbon-like elements that can “grow” into quite long and tangled), glass fibers in glass filled products, that can impede the flow of materials or even totally block the flow. The characteristics of such a transport system are quite well known, as is the importance and value of keeping product particles as free as possible of contaminants.
The term “contaminant” as used herein includes a broad range of foreign material and includes foreign material as well as broken particles or streamers of the product being transported. The generation of contaminants, also referred to as dust, can be from a large number of sources, including, in the way of examples, the creation of dust particles during the processing of plastic pellets in which the larger particles are segregated to be re-ground; organic matter in food grains, such as shells and hulls; the creation of dust in the formation of iron ore pellets; and, as noted previously, the mere conveyance of the pellets in pipes and other mechanical conveying and handling systems. Using plastics as an example, such foreign material could have a detrimental effect on the finished product. Specifically, foreign material different in composition from the primary material, such as dust, and non uniform material of the primary product, such as streamers, would not necessarily have the same melting temperatures as the primary product and would cause flaws when the plastics material is melted and molded.
Considering product quality, and focusing on moldable plastics as a primary example, foreign material different in composition from the primary material, such as dust, non-uniform material of the primary product, fluff, and streamers, does not necessarily have the same melting temperatures as the primary product and causes flaws when the material is melted and molded. These flaws result in finished products that are not uniform in color, may contain bubbles, and often appear to be blemished or stained, and are, therefore, unsellable. It is important to note that since these same non-uniform materials often do not melt at the same temperature as the primary product, the unmelted contaminants cause friction and premature wear to the molding machines, resulting in downtime, lost production, reduced productivity, increased maintenance and thus increased overall production costs.
Since dust and other contaminants are generated mostly by the transport system, it is of primary importance to not only provide apparatus for thoroughly cleaning the particles, but to do so as close to the point of use of the particles as possible so as to avoid the generation of contaminants through additional transport. Accordingly, compact dedusters have been used for many years to clean materials in this application, capable of handling smaller volumes of product, yet also capable of thoroughly cleaning the product. The compact dedusters permit the installation of the deduster immediately before final use of the products, such as being installed directly on top of molding machines or extruders, or on top of silos, as well as under silos, rather than at an earlier stage after which re-contamination can occur before the products are utilized. Of course, the dedusters can be installed as a free standing unit, as well.
Dedusters used to clean contaminants from particulate material can be found in U.S. Pat. No. 5,035,331, granted to Jerome I. Paulson on Jul. 30, 1991, in which air is blown upwardly through wash decks over which a flow of contaminated particulate material is passed so that the flow of air up through the wash decks removes the contaminants from the material flow. A magnetic field is provided by the deduster so that the particulate material flow passes through the magnetic field to neutralize the static charge on the particulates and facilitate the removal of the contaminants from the material. The flow of contaminant laden air is discharged from the deduster, while the cleaned particulate material is passed on to the manufacturing process.
A compact dedusting apparatus is disclosed in U.S. Pat. No. 6,595,369, granted on Jul. 22, 2003, to Jerome I. Paulson. Like the larger dedusting apparatus depicted in U.S. Pat. No. 5,035,331, the follow of particulate material is cleansed of contaminates that have had the static charged attracting the contaminates to the particulates neutralized. The cleaning process utilizes a flow of air passing through the stream of particulate material passing over wash decks. The contaminate-laden air is discharged through the top of the dedusting apparatus, while the cleaned particulate material is discharged from the bottom of the deduster.
These compact dedusters are provided with a single wash deck bathed in a magnetic flux field to provide dual action cleaning that fluidizes the flow of particles over the wash deck and uses a counter current flow to dislodge dust particles from the product for discharge from the apparatus. The magnetic flux field extends on opposing sides of the magnetic flux field generator, as well as above and below the magnet. Accordingly, a single wash deck is utilizing only a quarter of the magnetic flux filed that is generated. Furthermore, a single wash deck is limited in capacity. A double wash deck configuration is known from the Pelletron Max Series dedusters, wherein back to back wash decks are provided with a lower dust air outlet having a deflector panel to minimize the inadvertent discharge of cleaned particles with the dust-laden air being discharged from the lower air outlets.
The discharge of dust-laden air through the upper air discharge openings is a limiting factor to the capacity of the compact deduster to clean particles. If the velocity of the air passing through the wash decks and through the Venturi zone is too great, cleaned particles will be carried over into the discharged air flow. Thus, deflectors have been provided in an attempt to minimize product carryover and air velocity is closely controlled. The compact dedusters disclosed in the aforementioned Paulson patents represent a compact package in which highly efficient particle dedusting operations are conducted; however, some commercial or industrial applications for the dedusters require yet a smaller compact design, which exacerbates the aforementioned problems of capacity, carryover, and air velocity.
Accordingly, it would be desirable to provide a dedusting apparatus that is more compact than previously known without sacrificing capacity and preferably improving cleaning efficiencies.